Formaldehyde polymer stabilized by a poly



United States l atent OfiFice 3,318,397

Patented May 9, 1967 aldehyde having a molecular weight in the range from 3,318,970 about 10,000 to about 200,000 and a melting point above BSGESgg BY A 170 C., the predominant structural feature of both hmopolymers and copolymers being the recurring oxy- Rlchard l L 1 Tennem 5 methylene units (-OCH in the polymer chain. No gg igfig l dzggfizi ggz g ggfg Among the most important of the homopolymers are 12 Claims (CL 260 823) a,w-polyoxymethylene glycol, a,w-polyo xymethylene carboxylates (such as the diacetate or di-propionate), and This invention relates to the stabilization of polyac- -p0lyoxymethylene diethers (such as the methyl, ethyl, etals and, more particularly, to the stabilization of high or B-hydroxyethyl ether), each of which may have molecular weight polymers of formaldehyde. The invenbranches which comprise w-substituted polyoxymethylene tion provides an improved thermally stable polyacetal chains at one or more points in the main polymer chain. composition and is based on the discovery that certain Th formaldehyde copolymers include linear, branchedpoly(amide-acetals), when incorporated into high molec- Chain, and cross-linked polymers in which the recurring ular Weight polymers of formaldehyde, particularly in con- 15 y y n Bits z) in the p y chains junction with other stabilizers, are remarkably effective are periodically or randomly interrupted by other oxyalfor improving the thermal stability of the formaldehyde kylene Units Containing tWO mere Vieihal Ca n at m polymers, or by other units introduced by copolymerizing other Recent advances in polymer process technology have monomers, Such vy 'P 0r Y- made commercially available high molecular Weight polyanic acid, with substantially anhydrous formaldehyde or acetal resins. These polyacetal resins, which include both With its cyclic trimer, trioxane. The formaldehyde polythe homopolyrners and copolymers of formaldehyde, are mers also include linear and branched-chain terpolymers, thermoplastic resins which upon stabilization, may be such as those obtained by polymerizing trioxane with both fabricated into films, filaments, fibers, rods, and tubes. a menoeyehe ether (L and a dicy lic ethe Because of the inherent instability of unstabilized poly '(P y difofmal) Or other rp lymers. acetals (such as polyoxymethylene glycol) to oxidative The poly(amide-acetals) which are used to stabilize or hydrolytic cleavage of the polymer chains or to therg meleelllar Weight P y of formaldehyde in l d d i generally th raw d polycordance with the invention possess melting points in the mers require stabilization, either by the further reaction range from about C- tO out 200 C. and have a f an uncapped polymer by acylation, etherification, 0 molecular weight in the range from about 1,000 to about cyanaethylation, or cross-linking to block the uncapped These P Y(' are Polyamides Which hydroxyl groups to more stable groups, by t oll d contain one or more acetal units interposed in the polydegradation of the polymer chain until an end group is mef Chem Among the pelflamide'aeellals) Which have h d which i inert to f the h i or physical been used successfully to stabilize formaldehyde polymers degradation by the incorporation in the pogymer compoare those poly(amideacetals) containing the following sition of a stabilizer or stabilizer system which promotes unit! the stabilization of the polymer against oxidative, hydro- 043m CHM) lytic, or thermal degradation, or by employing a combi- .branched-chain homopolyrners and copolymers as well as C Using a large number of high molecular weight poly- 4O 0 -Ga CHz-O 0 i,,,

mers of formaldehyde including both linear and in which each x represents an integer in the range from 4 to- 16, y represents an integer in the range from 2 to 12, and m represents an integer in the range from 1 to 10. These poly(amide-acetals) may be conveniently prepared the capped and uncapped analogs of these polymers, I have found in all instances that the incorporation (or admixture) u formzfldahydfe pfflymer of a P Y by condensing a 3,9-bis-(w-carboxyalkylene)-2,4, 8,l0-tetaCetal) havlhg a meltlhg P 1n the range h ebellt raoxaspiro-[5,5]-undecane (or one of its lower' alkyl to ah011t200 and a moleellial' Weight n the esters) with an alkylene diamine, as illustrated by the range from about 1,000 to about 10,000 is remarkably f ll i equation; i

O *0113 GHQ-O O 1 ii 2)iOH H-c-(CHm-o-oR HgN-(OHzb-NH;

0-0112 CH2-O effective for improving the thermal stability of the form- In the foregoing equation, each R represents hydrogen or aldehyde polymer. Moreover, when the po1y(amidean alkyl group having from 1 to *6 carbon atoms, x and y acetal) is employed in the formaldehyde polymer with are integers having the aforementioned values, and n is other stabilizers, such as phenolic antioxidants, then the an integer in the range of approximately 3 to 30. Those stability of the resultant polyacetal composition is much poly(amide-acetals) in which each x is 7 and y is 6 have greater than can be obtained when any of these stabilizers been found to be especially effective as stabilizers for is employed by itself. Based on the results of an expolyacetal resins. ten sive series of experiments, it appears that stabilizer The 3,9 bis (w-carboxyalkylene)-2,4,8,10-tetra-oxasystems containing poly(amide-acetals) may be used to .spiro-[5,5]-undecanes which are used as the starting mastabilize any polyacetal composition containing a high terial in the preparation of these poly(amide-acetals) may molecular Weight polymer of formaldehyde. be prepared by reacting pentaerythritol and a dimethyl As used herein, the term high molecular weight polyacetal of a dialdehyde in accordance with the procedure rner of formaldehyde includes linear, branched-chain, described in the article by Pryde et al., Journal of Polymer and cross-linked homopolyrners and copolymers of form- Science, 58, 1 (1962). The preparation of poly(amideatmospheric, subatmospheric, or superatrnospheric pressure until a poly(amide-acetal) having the desired degree of polymerization is obtained. While substantially equivalent amounts of the cyclic acetal-dicarboxylic acid or its ester and the diamine are ordinarily used, a small excess, generally not more than 10 percent by weight, of either component can be used if desired.

The properties of these poly(amide-acetals) may be modified by substituting for a portion of the aforementioned cyclic acetal-dicarboxylic acid component an equivalent amount of a dicarboxylic acid (or diester) compound having the structural formula R-(i-(oH2)x( i-o-R in which each R and the x have the aforementioned significance. Preferably, these dicarboxylic acids (or diesters), if used, should be azelaic acid or dimethyl azelate for best results. In most cases, the cyclic acetal-dicarboxylic acid and the linear dicarboxylic acid starting materials are present in the reaction mixture in molar ratios of from approximately 1: to 10: 1.

While the properties of the poly(amide-acetals) are dependent upon the choice of reactants and the relative amount of each reactant that is used, these resinous products generally have melting points in the range of 150 C. to 200 C. and have molecular Weights between 1,000 and 10,000. Table I sets forth the properties of a number of poly(-amide-acetals) which have been used successfully to stabilize polyacetals in accordance with the invention. Included are a series of products prepared from 3,9-bis-(7- carbomethoxyheptyl) 2,4,8,l0-tetraoxaspiro-[5,5]-undecane (Compound A), dimethyl azelate (Compound B), and hexamethylene diamine, as well as one polymer in which Compound A was the sole dicarboxylic acid component used to prepare the poly(amide-acetal).

Table I .--Propertie's of poly(amide-ac erals) l Molar Ratio of Compound A to Compound B in Poly(amide-acetal) Melting Point Molecular Weight of Polyy- (amide-aeetal) (amide-acetal) Only very small amounts of the poly(amide-acetal) are required to stabilize the formaldehyde polymer, for concentrations as low as 0.1 percent by weight (based on the weight of the formaldehyde polymer) have been found to be effective. There appears to be no useful advantage in using more than about 30 percent by weight of the poly- (amide-acetal) stabilizer, and in general concentrations in the range from about 0.5 percent to about 20 percent by weight, based on the weight of the formaldehyde polymer, are sufficient to stabilize most high molecular weight polymers of formaldehyde.

Accordingly, the invention provides an improved thermally stable polyacetal composition comprising a high molecular weight polymer of formaldehyde having a molecular Weight in the range from about 10,000 to about 200,000 and a melting point above 170 C. and containing a stabilizer system comprising from about 0.1 to about 30 percent by weight, based on the weight of the formaldehyde polymer, of a poly(amide-acetal) having a melting point in the range from about C. to about 200 C. and a molecular weight in the range from about 1,000 to about 10,000. In the preferred embodiment of the invention, the poly(amide-acetals) are those polymers which are formed by reacting (i) a cyclic acetal having the structural formula wherein each R represents hydrogen or an alkyl group having from 1 to 6 carbon atoms and each x represents an integer in the range of 4 to 16, and (ii) an alkylene diamine having from 2 to 12 carbon atoms.

Although poly(amide-acetals) may be used as the .sole stabilizer in a polyacetal composition in accordance With the invention, their effectiveness is even more pronounced when these polymers are used in a stabilizer system which also contains an antioxidant. Suitable antioxidants include monocyclic phenols, such as hydroquinone and N- acyl-p-aminophenols, and alkylene-bis-phenols. Best results have been obtained by using stabilizer systems containing the poly(amide-acetal) together with an alkylenebis-phenol having the structural formula in which R and R" each represents an alkyl group having from 1 to 4 carbon atoms, and R' represents hydrogen or an alkyl group having from 1 to 3 carbon atoms. Among the many phenolic antioxidants which may be used in a stabilizer system together with the poly(amideacetals) in accordance with the invention are 2,2-methylene-bis-(4-methyl-6-tert. butylphenol), 6,6'-methylenebis-(3,4-xylenol), 2,2'-methylene-bis-(4-ethyl 6 tert. butylphenol), 4,4-methylene-bis-(2,6-di-tert. butylphenol), 6,6'-ethylidene-bis-(2,4-xylenol), 4,4'-ethylidenebis-(2,5-xylenol), 2,2'-ethylidene-'bis-(4-methyl 6 tert. butylphenol) *6,6-prop ylidene-bis- (2,4-xylenol) 4,4- butylidene-bis-(3-methyl-6-tert. butylphenol), 6,6'-butylidene-bis-(2,4-xylenol), 2,2-butylidine-bis-(4-tert. butyl 6-methylphenol), and 4,4-butylidene-bis-(2,5-xylenol). When used, the concentration of the antioxidant should be in the range from about 0.01 to about 10 percent by weight, based on the weight of the formaldehyde polymer and preferably in the range from about 0.1 to 0.5 percent by weight based on the weight of the formaldehyde polymer.

The optimum concentration ranges which are described above for the components of the stabilizer system have been found to be effective for enhancing the thermal stability of those high molecular weight polymers of formaldehyde in which they were tested. It should be realized, however, that the amount of each component that is used in the stabilizer system is dependent to a large extent upon the structure and chemical composition of the formaldehyde polymer. For example, if the formaldehyde polymer has been chemically stabilized by acetylation, etherification, or other reaction, a lower concentration of the stabilizer system may be used. Regardless of the degree of chemical stabilization of the formaldehyde polymer, the stabilizer system of the present invention may be used to improve the thermal stability of the resulting polyacetal composition whether or not the formaldehyde polymer has been stabilized by capping or partial depolymerization to more stable end groups.

The stabilizer system may be incorporated in the polyacetal compositions of this invention by any convenient procedure. For example, solutions of the stabilizer components in a volatile solvent, such as a ketone, lower alkanol, or chlorinated hydrocarbon, or a single solution bontaining both components can be added to the formaldehyde polymer in the amount that will provide the desired amounts of the stabilizer components in the poly- 'acetal composition, and the solvent removed by evaporation. Alternatively, the stabilized compositions can be 5 Percent LOSS prepared by milling the stabilizer components with the Example Stabilizer I1 1 Weight0f formaldehyde polymer or by dissolving both the stabilizer Stabmzed Polymer components and the formaldehyde polymer in a common solvent and then removing the Solvent y evaporation 3012122: 01383 332 3333 ;fiiiitstltiiz: iii? In addition to the formaldehyde polymer, poly(amide- None acetal), and an antioxidant, the polyacetal composition may also include plasticizers, fillers, pigments, and other EXAMPLE IV stabilizers, such as benzophenone derivatives which sta- A Series of o1 acetal co osition was re ared b bilize the polymer against degradation or discoloration the following grogedurez g by g of Z by ultravlolet hght' polyoxymethylene polyacetate having an average molecu- The following examples are illustrative of the eifeclat Weight of approximately 38 000 as determined y tiveness w which poly(a.lnide'acetals) may be incorpoviscometric techniques was added 1.5 parts by weight of Fined in hlgh molecular wfflght pi of formaldebyde a 1 percent solution in acetone of one of the poly(amideeither by themselves or in stabilizer systems containing acetals) described in Examples I and H and 03 part by other aiqqifives to prqpare thermally stable polyacetal weight of a 1 percent solution in acetone of 4,4-butylidenecompositions Of the lllventloni bis-(3-inethy1-6-tert. butylphenol). After air drying, the

EXAMPLE I thermal stability ratings of the resultant polyacetal com- 3,9Jbis (7 carbomethoxyheptyl) 2, 4,8110 tetraoxa positions were determined by the procedure set forth n spiro [55] undecane (4 grams, 0.008 mole) dimethyl gxlafnpllfl III, the results of these tests are summarized in azelate (17 grams, 0.08 mole), and hexamethylene dia e amine (10.4 gram 0.09 mole) were heated for four Table [IL-Thermal stability ratings of polyoxymethylene hours at 265-270 C. in an atmosphere of nitrogen and polyacetate compositions containing 1.5% by weight of then for an additional four hours at 270 C. and 19 mm. a p0ly(amide-acetal) and 0.3% by weight of 4,4- Hg, yielding a white polymeric product which was a butylidene-bis-(3-methyl-6-tert. butylphenol) hard, brittle solid that melted at 198199 C. Endgroup analysis by the procedure described by G. F. Price Percent LOSS in Techniques of Polymer Characterization, P. W. Example Poly(amide-acetal) InWeightof Allen, Ed., Butterworths, London, 1959, Chapter 7, in- Stablhzed Polymer dicated an amine content of 5.27 10- equivalent per 7 gram and a carbomethoxyl content of x we equive111; assesses; as: 3:3 alent per gram, which correspond to a molecular weight 40 None 17.6 of 3620 and about 12 repeating units.

E M E I 40 These examples illustrate the eflFectiveness with which 3,9 .biS (7 carbomethoxyheptyl) 2,438,) tetraoxa polyoxymethylene polyacetates may be stabilized with spiro-[5,5]-undecane (22.5) grams, 0.045 mole) d1- P 1y(amide-ace tals) which have been used alone and in methyl azelate (75 grams, 0.945 mole), and hexameth combination with antioxidants. E q ually satisfactory reylene diamine (10.4 grams, 0.09 mole) were heated for sults may be obtained in the stabilization of other high seven hours at ]60204 C. in an atmosphere of nitromolecular welght Polymers of foFmaldehyde suc h as the gen and then for an additional 2.5 hours at 197 -204 copolymers and terp1,ymers of Q and cychc i 0.6 mm Hg The White polymeric product was and consequently the invention s applicable to the stabilia hard, brittle Solid that melted at 1614630 C. zation of any high molecular weight polymer of formaldegroup analysis indicated an amine content of 3.33 10 hyde f a poly(amlde'acetal)' equivalent per gram and a carbomethoxyl content of I clam: H Q 30 1o4 equivalent per gram, which correspond to a 1. A thermally stable polyacetal composition compris molecular Weight of 5525 and about 14 repeating units. mg m1cu1ar we1,ght Polymer of formaldehyde having a molecular weight in the range from about 10,000 EXAMPLE III to about 200,000 and a melting point in excess of 170 C. Stabilized polyacetal compositions were prepared by and Containing a Stabilizer System Q P g from about the following procedure: To one part by weight of a to Percent, based on the Welght 0f the formaldepolyoxymethylene polyacetate having an average molecy P y in the Polyawtal composition, of 5 P 3- ular weight of approximately 30,000 as determined by (amide-Metal) having a melting Point in the range m viscometric techniques was added two parts by Weight about 150 C. to about 200 C. and a molecular weight of a 1 percent solution in acetone of one of the polyin the range from about 1,000 to about 10,000 and conamide acetals) described above. The resulting polyacetal taining a recurring unit having the structure I 0-0Hi CH2-O I 0H,),-OH CH-(CI g),CNH-(CHi)y-NH O OCfiz CHz-O H im composition was air-dried to remove the acetone, and the in which each x represents an integer in the range from thermal stability rating of the composition was then de- 4 to 16, y represents an integer in the range from 2 to 12, termined by measuring the weight loss that the stabilized and m represents an integer in the range from 1 to 10. polyacetal composition underwent on being heated in an 2. A thermally stable polyacetal composition comprisoxidizing atmosphere for 30 minutes at 222 C. The ing a high molecular weight polymer of formaldehyde results of these tests are summarized in Table II. having a molecular weight in the range from about 10,000

to about 200,000 and a melting point in excess of 170 C. andcontaining a stabilizer system comprising from about 0.1 to about 30 percent, based on the Weight of the formaldehyde polymer in the polyacetal composition, of a poly(amide-acetal) having a melting point in the range of approximately 150 C. to 200 C. and a molecular weight in the range of 1,000 to 10,000, said poly(amideacetal) being the polymeric product formed by reacting approximately stoichiometrically equivalent amounts of (a) a cyclic acetal having the structural formula ing a high molecular Weight polymer of formaldehyde having a molecular weight in the range from about 10,000 to about 200,000 and a melting point in excess of 170 C. and containing a stabilizer system comprising from about 0.1 to about 30 percent, based on the weight of the form- .aldehyde polymer in the polyacetal composition, of a poly(amide-acetal) having a melting point in the range from about 150 C. to about 200 C. and a molecular Weight in the range from about 1,000 to about 10,000, said poly(amide-acetal) being the polymeric product formed by reacting (a) a mixture of a cyclic acetal having the structural formula O-OH: CHz-O O ROi ](CH2)XC\ C\ OH(OH2)x-( JO-R and a dicarboxylic acid compound having the structural formula in both of which formulas R represents a member selected from the group consisting of hydrogen and alkyl groups having from 1 to 6 carbon atoms, and x is an integer from 4 to 16, the mole ratio of cyclic acid to dicarboxylic acid compound in the mixture being in the range from about 1110 to about 10: 1, together with approximately stoichiometrically equivalent amounts of (b) an alkylene diamine having from 2 to 12 carbon atoms.

4. A thermally stable polyacetal composition comprising a high molecular weight polymer of formaldehyde having a molecular weight in the range from about 10,000 to about 200,000 and a melting point in excess of 170 C. and containing a stabilizer system comprising from about 0.1 to about 30 percent, based on the weight of the formaldehyde polymer in the polyacetal composition, of a poly (amide-acetal) having a melting point in the range from about 150 C. to about 200 C. and a molecular weight in the range from about 1,000 to about 10,000, said poly(amide-acetal) being the polymeric product formed by reacting (a) a mixture of 3,9-bis-(7-carbomethoxyheptyl)-2,4,8,l0-tetraoxaspiro ,5 -undecane and dimethyl azelate in which the mole ratio of the cyclic acetal to dimethyl azelate is in the range from about 1:10 to about 102d, together with approximately a stoichiometrically equivalent amount of (b) an alkylene diamine having from 2 to 12 carbon atoms.

5. A thermally stable polyacetal composition according to claim 4, in Which the alkylene diamine used in the poly(amide-acetal) is hexamethylene tetramine.

6. A thermally stable polyacetal composition comprising a high molecular weight polymer of formaldehyde having a molecularweight in the range from about 10,000 to about 200,000 and a melting point in excess of 170 C.

and containing a stabilizer system comprising (a) from about 0.01 to about 10 percent by weight of an antioxidant, and (b) from about 0.5 to about 20 percent by Weight of a poly(amide-acetal) having a melting point in the range from about C. to about 200 C. and a molecular weight in the range from about 1,000 to about 10,000, said poly(amide-acetal) being the polymeric product formed by reacting (i) a mixture of a cyclic acetal having the structural formula and a dicarboxylic acid compound having the structural formula in both of which formulas R represents a member selected from the group consisting of hydrogen and alkyl groups having from 1 to 6 carbon atoms, and x is an integer from 4 to 16, the mole ratio of cyclic acid to dicarboxylic acid compound in the mixture being in the range from about 1:10 to about 10:1, together with approximately stoichiometrically equivalent amounts of (b) an alkylene diamine having from 2 to 12 carbon atoms, all percentages being based on the weight of the formaldehyde polymer in the polyacetal composition.

'7. A thermally stable polyacetal composition in ac cordance with claim 6, in which the antioxidant is an alkylene-bis-phenol having the structural formula in which R and R" each represents an alkyl group having from 1 to 4 carbon atoms, and R represents a member selected from the group consisting of hydrogen and alkyl groups having from 1 to 3 carbon atoms.

8. A thermally stable polyacetal composition in accordance With claim '6, in which the antioxidant is 4,4- butylidene-bis- 3-methyl-6-tert. butylphenol).

9. A thermally stable polyacetal composition in accordance with claim 6, in which the cyclic acetal used in the poly(amide-acetal) is 3,9-bis-(7-carbomethoxyheptyl) -2,4,8,l0-tetraoxaspiro- [5,5 -undecane.

10. A thermally stable polyacetal composition in accordance with claim 6, in which the dicarboxylic acid compound used in the poly(amide-acetal) is dimethyl azelate.

11. A thermally stable polyacetal composition in accordance with claim 6, in which the alkylene diamine used in the poly(amide-acetal) is hexamethylene diamine.

12. A thermally stable polyacetal composition cornprising a high molecular weight polymer of formaldehyde having a molecular weight in the range from about 10,000 to about 200,000 and a melting point in excess of C. and containing a stabilizer system comprising (a) from about 0.1 to about 0.5 percent by Weight of an alkylenebis-phenol having the structural formula in Which R and R each represents an alkyl group having from 1 to 4 carbon atoms, and R' represents a member selected from the group consisting of hydrogen and alkyl groups having from 1 to 3 carbon atoms, and (b) from about 0.5 to about 20 percent by weight of a poly(amideacetal) having a melting point in the range from about 150 C. to about 200 C. and a molecular weight in the range from about 1,000 to about 10,000, said poly(amideacetal) being the polymeric product formed by reacting (i) a mixture of 3,9-bis-(7-carbomethoxyheptyl)-2,4,8,10- tetraoxaspiro-[5,5]-undecane and dimethyl azelate in which the mole ratio'bf the cyclic acetal to dimethyl azelate is in the range from about 1:10 to about 10:1, together with approximately a stoichiometrically equivalent amount of (ii) hexamethylene diamine, all percentages being based on the weight of the formaldehyde polymer in the polyacetal composition.

References Cited by the Examiner UNITED STATES PATENTS 3,161,619 12/1964 Rice et a1. 260-78 3,223,683 12/1965 Pryde 260-78 

1. A THERMALLY STABLE POLYACETAL COMPOSITION COMPRISING A HIGH MOLECULAR WEIGHT POLYMER OF FORMALDEHYDE HAVING A MOLECULAR WEIGHT IN THE RANGE FROM ABOUT 10,000 TO ABOUT 200,000 AND A MELTING POINT IN EXCESS OF 170*C. AND CONTAINING A STABILIZER SYSTEM COMPRISING FROM ABOUT 0.1 TO 30 PERCENT, BASED ON THE WEIGHT OF THE FORMALDEHYDE POLYMER IN THE POLYACETAL COMPOSITION, OF A POLY(AMIDE-ACETAL) HAVING A MELTING POINT IN THE RANGE FROM ABOUT 150*C. TO ABOUT 200*C. AND A MOLECULAR WIEGHT IN THE RANGE FROM ABOUT 1,000 TO ABOUT 10,000 AND CONTAINING A RECURRING UNIT HAVING THE STRUCTURE 